“Dr. Paul will be his own man in Washington, not beholden to the special interests and beltway insiders who come looking for handouts on a daily basis,” said Bunning in a statement.

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Paul, a Bowling Green ophthalmologist and the son of former presidential candidate Rep. Ron Paul (R-Texas), is facing Secretary of State Trey Grayson in next month’s primary.

By declaring his preference for Paul to succeed him, Bunning is extracting a measure of political revenge.

The 77-year-old senator blamed McConnell and top national Republicans for pushing him to retire this year instead of seek a third term. Bunning raised little money before angrily declaring last year that he would not run for reelection.

Still, his move comes as a surprise because, before he announced last year that he’d bow out, Bunning also appeared to give his political blessing to Grayson, who created an exploratory committee only after meeting with the senator.

But Bunning has long been at odds with McConnell and, with Paul leading in many polls, plainly saw an opportunity to strike back at his rival and the leader of the Kentucky GOP and the Senate minority.

In the first sentence of the statement, Bunning said: “In the United States Senate, Kentuckians need a strong, principled conservative to stand up to the liberals and establishment politicians that run Washington.”

McConnell has not officially endorsed Grayson but his political operation is running the secretary of state’s campaign.

Bunning’s endorsement underlines Paul’s strong standing just over a month before the primary. Capturing support from many tea party activists, Paul has staked out an advantage over Grayson, the establishment-preferred candidate.

Recent automated polls show Paul enjoys a double-digit lead, even as Grayson hammers him in television ads.

Grayson’s campaign responded to the news with a mild shot at the baseball Hall of Famer.

"We’ve always respected Senator Bunning’s fiscally conservative views, but even as a major league pitcher, he’d occasionally misfire," said Grayson campaign manager Nate Hodson. "He is flat-out wrong about Rand Paul. Kentuckians need a fresh face, an outsider who can stand up for Kentucky values in Washington. Instead, as Rand Paul seeks to join the family business he has shown that he is well-versed in the ways of Washington and is willing to say anything for the sake of political expedience. His strange views on 9/11, Guantanamo, the wars in Iraq and Afghanistan, abortion and other issues simply do not match the views of Kentuckians."